The field of the invention relates to gyroscopes and more particularly to two-axis, flexure suspended gyroscopes.
A prior art gyroscope (gyro) configuration to which the present invention relates is shown in FIG. 1. In the illustrated arrangement the gyro torquer comprises a flywheel 1 which encloses a single radially oriented magnet 2. A shield plate 3, which acts as a pickoff return path, partially closes the open end of the flywheel. This type of wheel can be made to have a relatively low inertia and can be torqued at high rates. However, its disadvantages are: it has relatively high torquer non-linearity errors, high hysteresis errors and high bias instability.
Non-linearity errors are mainly caused by the magnetic field generated by the current flowing through the torquer coil 4 which tends to drive the coil within the wheel. This force, called the solenoid force, is defined by the equation F=K (NI).sup.2 dP/d.theta. where N is the number of turns in the coil, I the current, and dP/d.theta. is the change in the permeability of the coil relative to the wheel as a function of angle. The magnetic permeance to the torquer coil is high in this design because of the shield.
Hysteresis errors are caused by high levels of torquer coil current which magnetize some magnetic impurities in the coil cement, wire or support form 5. Some of this magnetization remains, even with no current flowing through the coil, and reacts with the flux from the magnet to cause a torque. In this design configuration there is an inherently greater field intensity near the magnet and shields which increases the torque, as compared with a balanced condition of field intensity.
The bias instability is due to the magnetic coupling between the torquer coil 4 and pickoff coil 4a. Part of the field 7 generated by the torquer coil section 6 passes through the wheel return path and through the pickoff poles 7a. This can cause a change in pickoff null as well as a hysteresis error.